Thursday, August 30, 2012

Late Blight on the Tomatoes

A little time has passed and I'm feeling like I'm ready to talk about it. 

At first, I was in denial.  I noticed some spots on the lower leaves of a few tomato plants, and did a little Googling.  I thought it could be late blight, but it could also be a late blight imitator.  Sometimes drought stress causes leaves to spot, and we had been less frequent with our watering.  The trick to distinguishing one from the other is that drought stress will result in spots on the edges of the leaves, while late blight spots can show up anywhere.  And late blight will have a fuzzy white appearance to it. I didn't see anything fuzzy, so I waited.

After a week or so it became more clear.  (These spots didn't start at the edge of the leaves.)

And, then things progressed.

The fruit started to show tell-tale signs of infection.
And I was very sad.  All eight of the tomato plants in the upper garden were showing signs of late blight, and more Googling told me that the right thing to do would be to bag all of the infected plants and bring them to the dump.  Late blight is an airborne disease, and wind will spread it to my other tomato plants, and to my neighbors.  But then I read a little further and it seemed the woman who writes one of the gardening blogs I follow (Skippy's Vegetable Garden) was suffering similarly, and she had decided to remove as many of the diseased leaves as possible, and leave the tomatoes to ripen.  She also sprayed with an organic copper fungicide to slow the spread of the disease.  I've bought some, but I have to admit I haven't used mine yet.

We removed many of the diseased leaves, and some of the tomatoes that were beyond saving, and we decided to wait.  This is what our upper garden looks like today.

This is what it looked like just a few short weeks ago.

There are a few tomatoes that don't have any blight damage, yet.  I'm waiting for them to ripen just enough so I can pick them and let them finish the job inside.  (I put them on the windowsill with fine results, though there are lots of other ways to do it, apparently better ways.) Other tomatoes have a little damage, but you can still eat the remaining, healthy part of the tomato with no ill effects.  For some of the gigantic tomatoes, I've sliced off a big hunk and still had plenty of large, healthy looking slices. 

What else have I learned?
  • The late blight won't overwinter in our garden.  It can only survive on live plant tissue.  Still, rotating crops (three years is ideal) is always good practice for preventing other diseases from coming back.
  • Late blight won't effect the seeds.  I can still save the seeds from some of the ripe tomatoes and have healthy tomatoes next year. 
  • Late blight spreads by air, usually during wet, humid summers.  It has definitely been a very humid summer here.  This is also another reason to water at the base of the plant, and in the morning, so the plants dry in the sun during the day.
  • You can prevent late blight by spacing your plants far apart, giving them plenty of air circulation, room to breathe.  We did not do that.
The University of Massachusetts Extension has a great late blight fact sheet, as does Cornell.

The five tomato plants in our lower garden are showing some signs of blight on the leaves, but we've been picking them off and it's been slower to spread, thanks to the mostly dry weather.  The fruit looks okay, so far.  This is where I should be spraying the copper fungicide, to preserve what I can.  I will do that today.

In the meantime, we still have lots of tomatoes to use up, and I've been trying out some new recipes.  I'll share a few soon. 


Tortla Dot said...

Love the way you think,
the way you write, and link!
You are so energetic and bright,
So sorry about the blight!

Jan said...

Thanks for the great information on late blight. I didn't plant any veggies this year but do plan on it next year and will be sure to keep in mind spacing my tomatoes and peppers far apart, watering only at the base (no overhead sprinkling) and being vigilant about looking for signs of infection and removal of leaves, etc.